1. Field of the Invention
The present invention relates to a novel process for the alkylation of hydrocarbons.
2. Description of the Prior Art
Within the framework of the present invention, the term alkylation refers to the reaction of a hydrocarbon, such as an aromatic or a saturated hydrocarbon, with an olefin. Without limiting the scope of the invention we will further illustrate the invention by discussing the alkylation of saturated hydrocarbons, in general branched saturated hydrocarbons, with an olefin to give highly branched saturated hydrocarbons with a higher molecular weight. This reaction is of interest because it makes it possible to obtain, through the alkylation of isobutane with an olefin containing 2-6 carbon atoms, an alkylate which has a high octane number and which boils in the gasoline range.
Unlike gasoline obtained by cracking heavier petroleum fractions such as vacuum gas oil and atmospheric residue, gasoline obtained by alkylation is essentially free of contaminants such as sulfur and nitrogen and so has clean burning characteristics. Its high anti-knock properties, represented by the high octane number, lessen the need to add environmentally harmful anti-knock compounds such as lead. Also, unlike gasoline obtained by reforming naphtha or by cracking heavier petroleum fractions, alkylate contains few if any aromatics or olefins, which, environmentally speaking, is a further advantage.
The alkylation reaction is acid-catalyzed. At present, in commercial alkylation equipment use is made of liquid acid catalysts such as sulfuric acid and hydrogen fluoride. The use of such catalysts is attended with a wide range of problems. For instance, sulfuric acid and hydrogen fluoride are highly corrosive, so that the equipment used has to meet high quality requirements. Since the presence of highly corrosive materials in the resulting fuel is objectionable, the remaining acid has to be removed from the alkylate. Also, because of the phase separations, which have to be carried out, the process is complicated and thus expensive. Besides, there is always the risk that toxic substances such as hydrogen fluoride will be emitted.
A newer development in this field is the use of solid acid catalysts, such as zeolite-containing catalysts. Thus WO 9823560 describes the use of a catalyst containing a zeolite, such as a Y zeolite, and a hydrogenation function, such as a Group VIII noble metal, e.g., platinum or palladium, and, optionally, a matrix material, such as alumina, in the alkylation of saturated hydrocarbons. Though the performance of this catalyst is satisfactory, there is still a need for further increase of catalytic activity, selectivity, and stability of these catalysts.
We have made a surprising discovery that satisfies the above need by choice of catalyst features as set forth in the following discussion.